1. Field of the Invention
This invention relates to selected copolymers of acrylic and/or methacrylic acid esters as flow improvers in crude petroleum oil and petroleum oil fractions thereof, and to petroleum oil compositions containing them.
2. Statement of Related Art
It is known that the flow properties of crude petroleum oil and/or mineral oil fractions thereof can be improved by using limited quantities of synthetic flow aids with them. As is known, the purpose of these flow aids is the reduction of the actual temperature below which solid components in the liquid hydrocarbon mixture--particularly higher paraffins, in some cases in combination with asphalts or other difficulty soluble components--crystallise out in such quantities that the ability of the hydrocarbon mixture to flow is permanently impaired. The temperatures referred to above are measured by known methods of measuring the pour-point or solidifying point. Each crude oil, or the mineral oil obtained from it, has by reason of its specific composition a characteristic pour-point, which however in many crude oils lies so low that no disadvantageous effect occurs during extraction and pipe-line transport. There are also, however, a whole series of mineral oil grades with a solidifying point above 10 .degree. C. Here the use of flow aids based on differential synthetic homo-polymers and/or copolymers may be advisable. There is extensive prior art with respect to these flow aids, which are also referred to as paraffin inhibitors, and are as a rule produced by the polymerization of olefinically unsaturated compounds, which contain at least partially unbranched saturated hydrocarbon chains with at least 18 carbon atoms. See, for example, U.S. Pat. No. 3,957,659, as well as U.S. Pat. Nos. 4,110,283; 3,904,385; 3,951,929; 3,726,653; 3,854,893; and 3,926,579. See also published German application no. 2 047 448.
In practice, particular difficulties arise when the characteristic pour-point of the crude oil or the mineral oil fractions to be treated reaches extremely high values, e.g. 25 .degree. C. or even 30 .degree. C. and over. Mineral oil substances of this type have a tendency toward rapid solidification even at ambient temperature. If, for example, pumping operations are interrupted even for only a short time or if during transport, temperature regions with comparatively low temperatures are crossed--for example by pipes in sea water regions--then there occurs rapid solidification of the hydrocarbon material into a mass which can no longer be pumped, and with it the blocking of pipes, pumps and the like. This problem is made more difficult in that to ensure the absence of solidification of the oil, it is often required in practice to lower the pour-points of the oils and oil fractions to values below 15 .degree. C. and especially to values below 12 .degree. C. or even below 10 .degree. C. It is clear then that technological difficulties arise when for example it is required that a characteristic pour-point of a crude oil of approximately 33 .degree. C. should drop to values below 10 .degree. C. As an additional difficulty it should also be noted here that a simple increase of the amount added of any pour-point improver does not in general result in a corresponding increased lowering of the pour-point. Interactions, not explained in detail, between the flow-aids and the solidifying constituents of the crude oil are probably responsible for a type of threshold effect for the intended result, and whereby the particular composition of the flow aid has a decisive influence on its effectiveness. In U.S. Pat. No. 4,663,491 mixed polymerizates are disclosed of n-alkyl-acrylates with at least 16 carbon atoms in the alcohol radical and maleic acid anhydride with molar ratios of n-alkyl-acrylate to maleic acid anhydride of 20:1 to 1:10. Compounds of this type are disclosed for use as crystallization inhibitors for crude oils containing paraffin. The operating examples therein relate to the use of corresponding copolymers in the molar ratio of acrylic acid ester to the maleic acid anhydride of from 1:1 to 8:1. Crude oils with characteristic solidifying points below 20 .degree. C. are predominately used. A table of values is given for India crude oil, which is known to be a particularly highparaffin starting material (disturbing paraffin content 15%) and has a characteristic solidifying point of 33 .degree. C. The optimal effectiveness of the mixed polymerizates used in this patent with respect to the lowering of the solidifying point of this starting material lies at the molar ratio of acrylic acid ester/maleic acid anhydride of 4:1. The lowest solidifying points adjusted here lie at 12 .degree. C. If the maleic acid anhydride proportion in the copolymerizate is further reduced, the addition of similar amounts results in a rise in the solidifying points of the India crude oil mixed with it, see e.g. Table 2.